Reporting from the eastern part of Sweden I can only agree with Neils listing, but I have to add the ground-elder 'Aegopodium podagraria'. This herb was originally introduced by medieval monks but has now spread in an invasive manner. And once established in your garden it is almost impossible to get rid off. A bit off-topic a Korean friend of mine told me that upon arrival to Sweden meeting all this ground-elder he felt like coming to paradise! Apparently this herb is much cherished as a food and medical herb in Korea where it is hard to grow! Per-Ake Stockholm-Sweden Zone: 5-6 Thats funny, here in Western Sweden ivy (Hedera helix) is quite rare and we're pleased to find ivy growing wild. Scotch broom (Cytisus scoparius) is more common but nontheless we were pleased when it turned up in our garden a few years ago, bird spread I imagine, it's doing well and as it's growing in a wild part it can stay. Our problem-invasives are for instance (I'm sure I'll miss some) Japanese rose (Rosa rugosa), Giant Hogweed (Heracleum mantegazzianum) Japanese Knotweed (Fallopia japonica) and False oat grass (Arrhenatherum elatius).